Microplastics and Copper Affect Zebrafish Behavior and Responses to Predation Threat.

Microplastics have been found in every part of the planet and in almost every tissue type that has been tested. They are a complex class of pollutants with multiple direct and indirect effects. There is an urgent and growing need to understand their toxicological impacts. Here we measured the effects of two size classes (13.2 µm ± 8.1 and 595.7 µm ± 187.3) of aged polyethylene microplastics, in the presence or absence of copper (10 μg/L), on the behavior of zebrafish and on their ability to respond to a conspecific alarm cue. Additionally, we measured the effects of the microplastics and copper on metal bioaccumulation and induction of metallothionein. Exposure to microplastics decreased the swimming speed of the zebrafish but may have reduced some of the effects of copper. Fish exposed to copper and microplastics had higher swimming velocities than fish exposed to copper alone. However, large microplastics also increased copper bioaccumulation and metallothionein production. Fish that were not exposed to copper decreased their swimming speed after addition of the alarm cue, but there was also an interaction with microplastics. Multivariate analysis of swimming behavior showed that fish exposed to small microplastics and copper formed a distinctive group after addition of the alarm, suggesting that it altered their behavioral responses. Our results show complex interactions between microplastics and copper and highlight the need for comprehensive risk assessment under different environmental scenarios. Fish rely on olfaction to find food and avoid predators. It is well established that metals can inhibit olfaction in fish. Microplastics may interact with metallic pollutants to increase their impact.